South Carolina Forestry Commission Best Management Practices

Stream Crossings

An effort has been made to italicize technical words or phrases and clearly define them in the glossary.

Stream crossings are sometimes necessary for access to forestlands. All crossings need to be planned to minimize environmental impacts. Specific practices are recommended in this section to assure minimum impacts on water flow and aquatic organisms. Bridges, culverts, and fords are all acceptable stream crossings when matched to the site and installed properly.

Bridge construction across navigable waterways is under the jurisdiction of the South Carolina Department of Health and Environmental Control DHEC.* (Opens in new window) Permanent bridges (those that would remain in place for a period greater than six months) must meet higher standards than temporary bridges. Anyone planning to construct a bridge across a navigable waterway must contact DHEC for permit application forms and technical design information.

*DHEC: 2600 Bull St., Columbia, S.C. 29201 (803-734-5360)

BMPs

Cross streams at right angles except where prevented by geologic features.

Keep approaches to stream crossings to as gentle a slope as practical.

Use drainage structures, such as water turnouts or broadbased dips, on both sides of a crossing as needed to prevent road and ditch runoff from entering the stream.

Temporary culverts are sized for storm flows with a two-year
-recurrence interval. Permanent culverts are sized for storm flows with 25-year-recurrence intervals. Multiple smaller culverts designed to carry equivalent water flow can be substituted for the above culvert sizes.

For example:

Two 48" culverts can be substituted for a 60" culvert. Two 54" culverts can be substituted for a 72" culvert.

An alternative is a combination of a smaller culvert and rock surfaced road dips where the culvert is sized for annual storm flows, and the rock surfaced road dip is designed to handle the flow from larger
storm events. Landowners are encouraged to contact a local U.S. Natural Resources Conservation Service representative or other qualified professional to design culverted crossings specifically for each site.